A practical. binaural recording unit was designed and manufactured t o extend the present day high quality sound recording-reproducing equipment development So as t o u t i l i z e some of the benefits inherent in a stereophonic system. A review of theoretical factors involved in binaural sound recording and reproduction is presented, with a description of t h e t e c h n i c a l equipment developed t o provide a high quality binaural system consistent with reasonable 0;verd.l equipment cost. Some novel problems and effects encountered i n the development program, as well as experiences with binaural recording techinques i n t h e f i e l d s of radio transmission, court room recording, and test instrtmentation, are described. View full abstract»

This paper deals with a t h e o r e t i c a l c i r c u i t analysis of a single-ended push-pull audio amplifier. Linear tube characteristics and small signals are assumed. The problem of impedance matching is first discussed. The properties and the requirements of a s a t i s f a c t o r y d r i v e r s t a g e are analyzed, and an output stage using an impedance matching output transformer is discussed. The effects of the plate-to-ground capacitance of t h e d r i v e r stage on the frequency-gain characteristic and of the choice of the tube and circuit parameters are analyzed. The paper concludes with some experimental results indicative of the inherent properties of the amplifier. In a r e c e n t a r t i c l e by Peterson and Sinclair,l special c i r c u i t s have been suggested by which a high fidelity, low d i s t o r t i o n audio amplifier can be constructed without using output transformers or i n which the requimrnents of an output transformer can be greatly simplified, The present a r t i c l e will give a t h e o r e t i c a l analysis of the b a s i c c i r c u i t used by Peterson and Sinclair. It will be observed that many desirable characte r i s t i c s of t h i s a m p l i f i e r c i r c u i t can be deduced from this analysis. View full abstract»

The fundamental resonance of loudspeakers is recognized by many as a source of annoyance. Usually this resonance can be damped electrically by suitable selection of the amplifier impedance. What is less well known is that damping can also be achieved by acoustical means incorporated into the loudspeaker or the enclosure. This paper deals with the theory and methods for providing acoustic damping. It is concluded that transient response of loudspeakers and enclosures can be effectively controlled by acoustic damping. Furthermore, the response-frequency characteristic of the loudspeaker system need not be adversely affected, and it actually may be improved. Loudspeakers with acoustic damping may operate from high-impedance amplifiers without "hang-over." Performance characteristics become largely independent of the amplifier impedance. Acoustic damping may be designed in a straightforward manner by ascertaining the acoustical constants and using standard experimental techniques of equivalent circuit analysis. We conclude, therefore, that acoustic damping for loudapeakers merits far more serious consideration than it has had heretofore. View full abstract»

An acoustic lens combined with a conical horn can be used to obtain a highly directional microphone without some of the disadvantages of the parabolic microphone. The directional characteristics can be calculated satisfactorily if one assumes that the horn provides uniform flooding of the lens aperture. View full abstract»

This Paper presents a useful "handbook type" equation for calculating a suitable self-bias resistor for a class A triode amplifier stage designed for maximum signal output. It is shown also that the loss in gain is six decibels, when the cathode resistor is not shunted by a by-pass capacitor. This information provides a timesaving method for determining the cathode resistor, with only a knowledge of plate resistance and transconductance, and without the necessity of a family of plate characteristic curves. View full abstract»

A system for recording and reproducing television signals by means of magnetic tape has been developed. This system will accommodate both monochrome and color pictures. For monochrome pictures, two channels are used, one for the video signal and one for the sound signal. These signals are recorded as two tracks on 1/4-inch magnetic tape. For color pictures, five channels are used: video channels for the color signals red, green and blue, the synchronizing channel, and an audio channel. These signals are recorded as five tracks on 1/2-inch magnetic tape. An electronic servomechanism provides the speed constancy required for the reproduction of television signals from magnetic tape. The present tape speed is 30 feet per second. The recorded and reproduced frequency band is over 3 megacycles. There is a description of a demonstration which included side-by-side showing of a direct picture, and the same picture recorded and immediately played back. View full abstract»

This paper describes many of the present recording techniques and the limitations of each. Limitations in regard to performance such as frequency response, signal-to-noise ratio, and speed stability are considered from the standpoint of the machine as well as the medium used in the recording process. Many of the present day applications of magnetic recording are discussed, including those of television recording and the application of magnetic recording to seismic exploration. View full abstract»

Organ music produced in small rooms having little natura1 reverberation can be enhanced by the addition of artitificial reverberation. A direct method of adding the aftersound to the electro-acoustic transducer itself is described. This is a contrast to the more conventional reverberation systems nploying driving transducers, time-delay means, pickup transducers, and mixing and amplifying circuits. Multiply resonant elical medanical delay lines store the energy and radiate it at a later time. In one model the coupling to the transducer is mechanical, .and in the other model acoustical coupling provides a number of practical and acoustical advantages. View full abstract»

A cable-less microphone system has been developed, Designed for general public address use, the system utilizes inductioncoupling between the transmitter and receiver, and requires no license. The subminiature transmitter is completely contained in a stick type microphone housing. It consists of a microphone, a five-tube, printed circuit frequency-modulated transmitter, a self-contained antenna inductor, and batteries, and weighs less than one pound. The system gives excellent performance with operating areas up to 5000 square feet. The development of the system and of the subminiature transmitter is discussed and the performance of the induction system is evaluated. View full abstract»

The relative advantages of perpendicular versus longitudinal recording have been re-evaluated in term of the electron-beam pickup. It is shown that dc response can be obtained only with perpendicular or transverse recarding, but because of other considerations longitudinal recording appears to be more generally practicable, even though the resulting low-frequency response limit depends upon the extent to which the physical dimensions of the core may , b e increased and the speed of the recording medium may be reducqd. Measurement techniques have been devised to permit study of the magnetic circuit parameters which influence over-all pickup sensitivity; associated studies show the advantages of a core structure having unconventional configuration and physical dimensions. Procedures recentlypresented by other writers for the investigation of factors contributing t o high-frequency loss in conventional heads have been tested with the electron-beam pickup; tape-coating thickness appears to be responsible fm, a decibel loss approximately equal to the total contributed by all other factors. Relatively simple striptype core structures for use with the electron-beam tube have been developed - over-all performance data under typical recording conditions show an output of the order of 0.2 volt and an equalized response range of approximately one to 15,000 cycles per second, plus or minus three decibels, at a tape speed of 10 inches per second. View full abstract»

In keeping with the PGA policy of including, from time to time, subjects outside of the strict boundaries of technology, we have invited Dr. Kent to submit his very fine review of Electronic Music. Future developments in Audio techniques, and, therefore, this subject is bound to be of interest to all PGA members. -- Editorial Committee. View full abstract»